The present invention relates to hybrid drive systems for motor vehicles. More specifically, the present invention relates to a transfer case for use in four-wheel drive hybrid vehicles.
Automobile manufacturers are actively working to develop alternative powertrain systems in an effort to reduce the level of pollutants exhausted into the air by conventional powertrains equipped with internal combustion engines. Significant development has been directed to electric vehicles and fuel cell vehicles. Unfortunately, these alternative powertrain systems suffer from several disadvantages and, for all practical purposes, are still under development. However, several different hybrid electric vehicles (HEV) have recently been offered for sale. These hybrid vehicles are equipped with an internal combustion engine and an electric motor that can be operated independently or in combination to drive the vehicle.
There are two types of hybrid vehicles, namely, series hybrid and parallel hybrid. In a series hybrid vehicle, power is delivered to the wheels by the electric motor which draws electrical energy from the battery. The engine is used in series hybrid vehicles to drive a generator which supplies power directly to the electric motor or charges the battery when the state of charge falls below a predetermined value. In parallel hybrid vehicles, the electric motor and the engine can be operated independently or in combination pursuant to the running conditions of the vehicle. Typically, the control strategy for such parallel hybrid vehicles utilizes a low-load mode where only the electric motor is used to drive the vehicle, a high-load mode where only the engine is used to drive the vehicle, and an intermediate assist mode where the engine and electric motor are both used to drive the vehicle. Regardless of the type of hybrid drive system used, hybrid vehicles are highly modified versions of conventional vehicles that are expensive due to the componentry, required control systems, and specialized packaging requirements.
Hybrid vehicles have also been adapted to four-wheel drive vehicles and typically utilize the above-noted parallel hybrid powertrain to drive the primary wheels and a second electric motor to drive the secondary wheels. Obviously, such a four-wheel drive system is not only extremely expensive and difficult to package, but is also difficult to control in view of the need to react to instantaneous instances of wheel slip. Thus, a need exists to develop hybrid powertrains for use in four-wheel drive vehicles that utilize many conventional powertain components so as to minimize specialized packaging and reduce cost.
It is therefore an object of the present invention to provide a hybrid powertrain or drive system for a four-wheel drive vehicle.
In accordance with another object, the four-wheel drive hybrid drive system of the present invention includes a transfer case adapted for conventional connection between the transmission and the front and rear drivelines of the motor vehicle.
According to another object, the four-wheel drive hybrid drive system is a parallel-type system with an input clutch and an electric motor/generator integrated into the transfer case.
As a related object, the hybrid drive system of the present invention permits use of the internal combustion engine and the electric motor/generator separately or in combination as power sources for driving the motor vehicle.
These and other objects are provided by a transfer case comprised of a planetary gearset having a first input driven by the motor/generator, a second input driven by the transmission, and an output directing drive torque to the front and rear drivelines. The output of the planetary gearset drives a rear output shaft connected to the rear driveline and further drives a front output shaft connected to the front driveline. The transfer case further includes a second planetary gearset having an input driven by the motor/generator and an output driving the first input of the first planetary gearset.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are intended for purposes of illustration only since various changes and modifications within the scope of this particular invention will become apparent to those skilled in the art.